This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-371781, filed Dec. 6, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor integrated circuit, particularly to a technique for stabilizing an oscillation frequency of a voltage controlled oscillator (VCO).
2. Description of the Related Art
A voltage controlled oscillator is broadly used for a purpose of generating an internal clock for driving LSI such as a microcomputer, digital signal processor (DSP), or music, movie playback system such as a compact disc (CD) or digital versatile disc (DVD).
A proposal concerning a structure of the VCO has been presented by U.S. Pat. No. 5,594,391 by Yoshizawa and U.S. Pat. No. 5,955,929 by Moon et al.
However, a voltage controlled oscillator is easily influenced by noise of a power source, and the oscillation frequency of the clock sometimes fluctuates due to this the mixed noise. The fluctuation of the oscillation frequency can cause malfunctions in a semiconductor integrated circuit such as a microcomputer, or DSP operated by the clock generated by the voltage controlled oscillator.
A voltage controlled oscillator according to an aspect of the present invention comprises:
an oscillation controller constituted to generate first and second control potentials corresponding to an input voltage;
first and second current sources configured to generate control currents corresponding to the first and second control potentials, respectively;
an oscillation section, connected to a power source potential node via the first current source and connected to a ground potential node via the second current source, the oscillation section generating a clock whose oscillation frequency is determined by the control current;
a first fluctuation transmitter, disposed between the power source potential node and the first control potential node, the first fluctuation transmitter transmitting a potential fluctuation generated in the power source potential node to the first control potential node at the same phase and maintaining a potential difference between the power source potential and the first control potential to be constant; and
a second fluctuation transmitter, disposed between the ground potential node and the second control potential node, the second fluctuation transmitter transmitting the potential fluctuation generated in the ground potential node to the second control potential node at the same phase and maintaining the potential difference between the ground potential and the second control potential to be constant.
A delay circuit according to an aspect of the present invention comprises:
first and second inverter circuits each having a power source terminal and a ground terminal, the first and second inverter circuits outputting a reverse signal of an input signal after a delay time;
a first current source, disposed between the power source terminals of the first and second inverter circuits and a power source potential node, the first current source generating a first control current, which determines the delay time, based on a first control potential applied from the outside and preventing a noise superimposed on the power source potential node from being mixed into the power source terminal;
a second current source, disposed between the ground terminals of the first and second inverter circuits and a ground potential node, the second current source generating a second control current, which determines the delay time together with the first control current, based on a second control potential applied from the outside and preventing a noise superimposed on the ground potential node from being mixed into the ground terminal;
a first fluctuation transmitter, disposed between the power source potential node and the first control potential node, the first fluctuation transmitter transmitting a potential fluctuation generated in the power source potential node to the first control potential node at the same phase and maintaining a potential difference between the power source potential and the first control potential to be constant; and
a second fluctuation transmitter, disposed between the ground potential node and the second control potential node, the second fluctuation transmitter transmitting the potential fluctuation generated in the ground potential node to the second control potential node at the same phase and maintaining the potential difference between the ground potential and the second control potential to be constant.
A disc playback system according to an aspect of the present invention comprises:
a voltage controlled oscillator configured to generate an internal clock; and
a semiconductor circuit configured to operate in response to the internal clock,
the voltage controlled oscillator including:
an oscillation controller configured to generate first and second control potentials corresponding to an input voltage;
first and second current sources configured to generate control currents corresponding to the first and second control potentials, respectively;
an oscillation section, connected to a power source potential node via the first current source and connected to a ground potential node via the second current source, the oscillation section generating the internal clock whose oscillation frequency is determined by the control current;
a first fluctuation transmitter, disposed between the power source potential node and the first control potential node, the first fluctuation transmitter transmitting a potential fluctuation generated in the power source potential node to the first control potential node at the same phase and maintaining a potential difference between the power source potential and the first control potential to be constant; and
a second fluctuation transmitter, disposed between the ground potential node and the second control potential node, the second fluctuation transmitter transmitting the potential fluctuation generated in the ground potential node to the second control potential node at the same phase and maintaining the potential difference between the ground potential and the second control potential to be constant.